1. Field of the Invention
The present invention relates to an apparatus for quickly blowing a large quantity of compressed air to the surface of molding sand for use in a green sand mold molding facility in such a manner that compressed air is blown to the surface of the molding sand present in a mold flask to penetrate the molding sand before compressed air is discharged from a pattern plate so as to previously compress the molding sand before the molding sand is further compressed.
2. Related Art Statement
A green sand mold molding facility has been disclosed in Japanese Utility Model Laid-Open No. 1-80247. According to this disclosure, the green sand mold molding facility is arranged in such a manner that a cover member and a compressed air reserving tank having a compressed air outlet on the bottom plate thereof are disposed above a table for lifting a pattern plate on which a flask is placed. Furthermore, the above-described outlet is arranged in such a manner that it is opened/closed by a valve which is moved upwards/downwards when an air pressure cylinder performs extension/retraction of its piston rod. In addition, molding sand is injected into the flask before the upper end opening formed in the flask is closed by a cover member and as well as the tank is positioned on the cover member before the air pressure cylinder is operated to open the outlet formed in the bottom plate of the tank. As a result, compressed air in the tank is blown to the flask via the cover member to compress the molding sand and as well as penetrate the molding sand before the compressed air is discharged from the pattern plate. Then, compaction is performed by using a squeeze plate to compact and solidify the molding sand so that the green sand mold is molded.
In a green sand mold molding facility of the above described type, a large quantity of compressed air must be quickly blown to the molding sand placed in the flask. However, since the air pressure cylinder is communicated with a compressed air source via pipes, a switch valve and the like, the resistance caused by a residual compressed air which is inevitably present in the conduit and the inherent resistance of the pipe line causes, at the time of the operation of the air pressure cylinder, the operational speed to be lowered. As a result, the outlet cannot be opened at high speed to quickly blow the large quantity of compressed air, causing a problem in that the green sand mold molding facility cannot exhibit a high molding performance.
It is preferable that compressed air is introduced from the compressed air tank into the flask via a large-diameter cylindrical member. In order to achieve this, a large-diameter opening/closing valve must be provided for the cylindrical member to operate the opening/closing valve at a high speed. In order to operate the above-described opening/closing valve, excessively large power source must be provided. Furthermore, if a small gap is formed between the opening/closing valve and its seating portion at the time of initiation of the valve opening operation, compressed air is undesirably introduced through the above-described gap into the flask. Therefore, there arises another problem in that compressed air blown into the flask cannot be diffused equally and thereby the molding sand cannot be compacted down uniformly.